WASHINGTON - An experimental laser system is able to distinguish chemicals from hundreds of metres away and could be able to identify explosives and other dangerous compounds from a safe distance.
The system can distinguish different white powders that are optically and chemically similar from 400 metres off, the research team led by Brett Hokr of the A&M University in College Station, Texas said.
They published their findings in the Proceedings of the National Academy of Sciences.
The Hokr's team made use of an effect known as Raman scattering, where light is scattered from the atoms or molecules of a substance, with its wavelength undergoing a small change, depending on the chemical composition of the material.
The effect has long been known, but it is extremely weak. Only one in 10 billion photons is scattered in this way, meaning that detecting these photons from a distance is virtually impossible.
A few years ago, scientists discovered that Raman scattering is considerably boosted with a laser beam with the right characteristics and that it can itself take the form of a laser.
This so-called "Raman lasing" results in a much clearer signal being emitted from the test substance that can be detected from a distance.
The team used this effect to create a remote detection system, beaming a special laser at various white powders of similar chemical composition.
From a distance of 400 metres they were able to reliably distinguish barium sulphate (BaSO4), sodium nitrate (NaNO3), potassium nitrate (KNO3) and ammonium nitrate (NH4NO3).
Identification from up to a kilometre should be possible once the device has been optimised, Hokr's team said.